1. Field of the Invention
This invention relates to a semiconductor laser apparatus. This invention particularly relates to a surface emission type of semiconductor laser apparatus, in which a semiconductor laser device is employed as a pumping beam source.
2. Description of the Related Art
With the rapid advances made in functions and performance of optical information processing apparatuses, image processing apparatuses, printing apparatuses, and the like, in recent years, there has arisen a strong demand for semiconductor laser devices having high output power and capable of producing laser beams of high quality.
As a short-wavelength semiconductor laser device, which produces a laser beam having a wavelength of a 410 nm band, there has heretofore been proposed a semiconductor laser device comprising a GaN substrate, an n-GaN buffer layer, an n-InGaN anti-cracking layer, an AlGaN/n-GaN modulation-doped superlattice cladding layer, an n-GaN optical waveguide layer, an undoped InGaN/n-InGaN multiple quantum well active layer, a p-AlGaN carrier blocking layer, a p-GaN optical waveguide layer, an AlGaN/p-GaN modulation-doped superlattice cladding layer, and a p-GaN contact layer, which layers are formed on the GaN substrate. The GaN substrate is obtained by forming GaN on a sapphire substrate, growing GaN by the utilization of selective growth and by use of SiO2 as a mask, and thereafter separating the sapphire substrate. Such a semiconductor laser device is reported in, for example, xe2x80x9cJpn. J. Appl. Phys.,xe2x80x9d vol. 37, pp. L1020, 1998. However, with the proposed semiconductor laser device, wherein a stripe width is as narrow as 2 xcexcm, only an optical output power of as low as 100 mW can be obtained.
As for a semiconductor laser device for producing a red laser beam, it has been reported in, for example, xe2x80x9cIEEE Photonics Technology Letters,xe2x80x9d Vol. 11, pp. 791, 1999, that a single-mode semiconductor laser, which produces a laser beam having a wavelength of 660 nm with an output power of 400 mW, has been achieved. However, the reported semiconductor laser device has the problems in that a side lobe arises in a transverse mode, and good beam characteristics cannot be obtained. Also, though the reported semiconductor laser device has a broad area structure, the reported semiconductor laser device has the problems in that, since the end face optical density is high, it is difficult for the output power to be enhanced even further, and the reliability with the passage of time is low. As for single-stripe semiconductor laser devices for producing a red laser beam, attempts have heretofore been made to employ a window structure for enhancing the output power and accomplishing oscillation in a fundamental mode. However, currently, with the single-stripe semiconductor laser devices for producing a red laser beam, which have the window structure, the output power is practically limited to approximately 50 mW.
Different examples of techniques for enhancing the output power include semiconductor laser pumped second-harmonic-generation (SHG) solid lasers. However, the semiconductor laser pumped SHG solid lasers have the problems in that, since the life of the fluorescence produced by the rare earth element of the laser crystal is markedly long, it is difficult for the laser beam produced by the solid laser to be modulated quickly with direct modulation of the pumping semiconductor laser. Also, the semiconductor laser pumped SHG solid lasers have the problems in that, since the second harmonic is utilized, the efficiency cannot be kept high.
As a laser device having a high output power and undergoing oscillation in a fundamental transverse mode, a semiconductor laser pumped, surface emission type of laser device, in which an AlGaAs type of semiconductor is employed, is described in, for example, U.S. Pat. No. 5,627,853. However, in U.S. Pat. No. 5,627,853, as for a technique for producing a laser beam having a wavelength shortened even further, it is described only that the SHG is utilized. In U.S. Pat. No. 5,627,853, nothing is described about a surface emission type of laser device, which produces a laser beam having a short wavelength with a high efficiency and in which the SHG is not utilized.
As lasers for producing a laser beam having a wavelength of an ultraviolet region, solid lasers, which produces a laser beam having a wavelength shorter than 400 nm and utilizes third harmonic generation (THG) driven in a pulsed mode, have heretofore been used in practice. However, the solid lasers utilizing the THG have the problems in that the efficiency cannot be kept high in producing a continuous wave (CW) with the THG, and therefore the solid lasers are not practical. Also, in order for the oscillation in the CW mode of the THG to be achieved at a high efficiency, the second harmonic of the fundamental wave must be resonated. In such cases, the temperature of the resonator must be controlled at a markedly high accuracy of within 0.01xc2x0 C. The strict control requirement also makes the solid lasers utilizing the THG unpractical. Further, as a different technique for producing a laser beam having a wavelength of the ultraviolet region, it may be considered to obtain an ultraviolet laser beam having a wavelength shorter than 400 nm with the generation of the second harmonic of a beam produced by a Cr:LiSAF or Cr:LiCAF crystal. However, in such cases, since re-absorption of the beam produced by the Cr:LiSAF or Cr:LiCAF crystal occurs, it is difficult for a beam having a wavelength falling within the range of 700 nm to 800 nm to be produced efficiently.
Also in U.S. Pat. No. 5,627,853, nothing is described about a laser device for producing a laser beam having a wavelength of the ultraviolet region.
As described above, with the conventional semiconductor laser devices for producing a laser beam having a wavelength of the red region, it is difficult for a high output power and oscillation in the fundamental mode to be obtained.
Also, as for the laser devices for producing a laser beam having a wavelength of the ultraviolet region, a high-efficiency wavelength converting laser, in which a surface emission laser is utilized and the SHG of the ultraviolet region is utilized, has not been proposed in the past.
The primary object of the present invention is to provide a semiconductor laser apparatus, which produces a laser beam having a wavelength of a red region, and which undergoes oscillation in a fundamental mode with a high reliability and a high efficiency and up to a high output power.
Another object of the present invention is to provide a semiconductor laser apparatus, which produces a laser beam having a wavelength of an ultraviolet region, and which undergoes oscillation in a fundamental mode with a high reliability and a high efficiency and up to a high output power.
The present invention provides a first semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of InGaN and GaN is employed in an active layer, and
ii) a surface emission type of semiconductor device comprising:
a) a substrate, and
b) an active layer, which is constituted of a composition selected from the group consisting of InGaAlP and InGaP and is provided on the substrate,
the surface emission type of semiconductor device being pumped by the pumping beam source to produce a laser beam.
InGaN generally means compounds represented by InXGa1xe2x88x92XN (where 0 less than X less than 1).
The present invention also provides a second semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of InGaN and GaN is employed in an active layer, and
ii) a surface emission type of semiconductor device comprising:
a) a substrate,
b) a semiconductor layer, which is overlaid on the substrate and contains an active layer constituted of a composition selected from the group consisting of InGaAlP and InGaP, and
c) mirrors, each of which is provided on one of two opposite end faces of the semiconductor layer, the two opposite end faces being taken with respect to a direction of overlaying of the semiconductor layer,
InGaAlP and InGaP generally mean compounds represented by InX(GaYAl1xe2x88x92Y)1xe2x88x92XP and InXGa1xe2x88x92XP, respectively, where 0 less than X less than 1 and 0 less than Y less than 1.
the surface emission type of semiconductor device being pumped by the pumping beam source to produce a laser beam.
The present invention further provides a third semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of GaNAs and InGaNAs is employed in an active layer, and
ii) a surface emission type of semiconductor device comprising:
a) a substrate, and
b) an active layer, which is constituted of a composition selected from the group consisting of InGaAlP and InGaP and is provided on the substrate,
the surface emission type of semiconductor device being pumped by the pumping beam source to produce a laser beam.
The present invention still further provides a fourth semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of GaNAs and InGaNAs is employed in an active layer, and
ii) a surface emission type of semiconductor device comprising:
a) a substrate,
b) a semiconductor layer, which is overlaid on the substrate and contains an active layer constituted of a composition selected from the group consisting of InGaAlP and InGaP, and
c) mirrors, each of which is provided on one of two opposite end faces of the semiconductor layer, the two opposite end faces being taken with respect to a direction of overlaying of the semiconductor layer,
the surface emission type of semiconductor device being pumped by the pumping beam source to produce a laser beam.
GaNAs and InGaNAs generally mean compounds represented by GaNXAs1xe2x88x92X and InYGa1xe2x88x92YNXAs1xe2x88x92X, respectively, where 0 less than X less than 1 and 0 less than Y less than 1.
The present invention also provides a fifth semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of InGaN and GaN is employed in an active layer,
ii) a surface emission type of semiconductor device comprising:
a) a substrate,
b) an active layer, which is constituted of a composition selected from the group consisting of InGaAlP and InGaP and is provided on the substrate, and
c) a mirror, which is formed on a substrate-facing side of the active layer of the surface emission type of semiconductor device or the other side of the active layer opposite to the substrate-facing side,
the surface emission type of semiconductor device being pumped by the pumping beam source, and
iii) an external mirror, which is located at an exterior of the surface emission type of semiconductor device and constitutes a resonator in co-operation with the mirror of the surface emission type of semiconductor device,
a laser beam being radiated out from the external mirror.
The present invention further provides a sixth semiconductor laser apparatus, comprising:
i) a pumping beam source constituted of a semiconductor laser device, in which a composition selected from the group consisting of GaNAs and InGaNAs is employed in an active layer,
ii) a surface emission type of semiconductor device comprising:
a) a substrate,
b) an active layer, which is constituted of a composition selected from the group consisting of InGaAlP and InGaP and is provided on the substrate, and
c) a mirror, which is formed on a substrate-facing side of the active layer of the surface emission type of semiconductor device or the other side of the active layer opposite to the substrate-facing side,
the surface emission type of semiconductor device being pumped by the pumping beam source, and
iii) an external mirror, which is located at an exterior of the surface emission type of semiconductor device and constitutes a resonator in co-operation with the mirror of the surface emission type of semiconductor device,
a laser beam being radiated out from the external mirror.
The first, second, third, fourth, fifth, and sixth semiconductor laser apparatuses in accordance with the present invention should preferably be modified such that the semiconductor laser device is provided with a stripe-shaped electric current injection window, and a stripe width constituting the electric current injection window is at least 5 xcexcm.
Also, in the first, second, third, fourth, fifth, and sixth semiconductor laser apparatuses in accordance with the present invention, the laser beam should preferably have a wavelength falling within the range of 600 nm to 700 nm.
The present invention still further provides a seventh semiconductor laser apparatus, comprising:
i) a semiconductor laser device, in which a GaN type of semiconductor is employed as an active layer,
ii) a surface emission type of semiconductor device, in which a semiconductor selected from the group consisting of an InGaAlP type of semiconductor and an InGaP type of semiconductor is employed as an active layer,
the surface emission type of semiconductor device being pumped by the semiconductor laser device, and
iii) wavelength converting means for converting a wavelength of light obtained through the pumping and radiating out a laser beam having a wavelength of an ultraviolet region.
In the seventh semiconductor laser apparatus in accordance with the present invention, the active layer of the semiconductor laser device may have a composition selected from the group consisting of InGaN and GaN. Alternatively, in the seventh semiconductor laser apparatus in accordance with the present invention, the active layer of the semiconductor laser device may have a composition selected from the group consisting of GaNAs and InGaNAs.
The present invention also provides an eighth semiconductor laser apparatus, comprising:
i) a semiconductor laser device, in which a GaN type of semiconductor is employed as an active layer,
ii) a surface emission type of semiconductor device, in which a GaN type of semiconductor is employed as an active layer,
the surface emission type of semiconductor device being pumped by the semiconductor laser device, and
iii) wavelength converting means for converting a wavelength of light obtained through the pumping and radiating out a laser beam having a wavelength of an ultraviolet region.
In the eighth semiconductor laser apparatus in accordance with the present invention, the active layer of the semiconductor laser device may have a composition selected from the group consisting of InGaN, GaN, GaNAs, and InGaNAs.
With the first, second, and fifth semiconductor laser apparatuses in accordance with the present invention, the semiconductor laser device, in which the active layer is constituted of the composition selected from the group consisting of InGaN and GaN, is employed as the pumping beam source, and laser oscillation is obtained with the surface emission type of semiconductor device, in which the active layer is constituted of the composition selected from the group consisting of InGaAlP and InGaP. Therefore, a broad area type of semiconductor laser device can be utilized as the pumping semiconductor laser device, and a high output power falling within the range of, for example, 1 W to 10 W can be obtained with the semiconductor laser device. Accordingly, a semiconductor laser apparatus, which produces a laser beam having a wavelength of the red region and has an output power falling within the range of several hundreds of milliwatts to several watts, can be obtained.
Also, with the first, second, and fifth semiconductor laser apparatuses in accordance with the present invention, wherein the semiconductor laser device is employed as the pumping beam source, side mode-free oscillation in the fundamental transverse mode can be obtained with a high output power.
With the third, fourth, and sixth semiconductor laser apparatuses in accordance with the present invention, wherein the active layer of the semiconductor laser device is constituted of the composition selected from the group consisting of GaNAs and InGaNAs, as in the first, second, and fifth semiconductor laser apparatuses in accordance with the present invention, side mode-free oscillation in the fundamental transverse mode can be obtained, and a laser beam having a wavelength of the red region can thereby be produced.
With the fifth and sixth semiconductor laser apparatuses in accordance with the present invention, wherein the resonator is formed by the provision of the external mirror, even if a side lobe occurs, the side lobe can be restricted by inserting a slit, or the like, into the resonator.
The seventh semiconductor laser apparatus in accordance with the present invention for producing a laser beam having a wavelength of the ultraviolet region comprises the semiconductor laser device, in which the GaN type of semiconductor is employed as the active layer, and the surface emission type of semiconductor device, in which the semiconductor selected from the group consisting of the InGaAlP type of semiconductor and the InGaP type of semiconductor is employed as the active layer, the surface emission type of semiconductor device being pumped by the semiconductor laser device. The seventh semiconductor laser apparatus in accordance with the present invention also comprises the wavelength converting means for converting the wavelength of light obtained through the pumping and radiating out the laser beam having a wavelength of the ultraviolet region. Therefore, with the seventh semiconductor laser apparatus in accordance with the present invention, a laser beam, which is produced by the semiconductor laser device and has a wavelength of the 400 nm band, is absorbed by the surface emission type of semiconductor device, and light having a wavelength falling within the range of 600 nm to 700 nm is radiated out from the surface emission type of semiconductor device. The light radiated out from the surface emission type of semiconductor device is subjected to wavelength conversion, and a laser beam having a wavelength of the ultraviolet region can thereby be obtained.
The eighth semiconductor laser apparatus in accordance with the present invention for producing a laser beam having a wavelength of the ultraviolet region comprises the semiconductor laser device, in which the GaN type of semiconductor is employed as the active layer, and the surface emission type of semiconductor device, in which the GaN type of semiconductor is employed as the active layer, the surface emission type of semiconductor device being pumped by the semiconductor laser device. The eighth semiconductor laser apparatus in accordance with the present invention also comprises the wavelength converting means for converting the wavelength of light obtained through the pumping and radiating out the laser beam having a wavelength of the an ultraviolet region. Therefore, with the eighth semiconductor laser apparatus in accordance with the present invention, the surface emission type of semiconductor device, in which the GaN type of semiconductor is employed as the active layer, is pumped by a pumping beam, which is produced by the GaN type of semiconductor laser device and has a wavelength of the 380 nm band, and light having a wavelength falling within the range of 400 nm to 560 nm is radiated out from the surface emission type of semiconductor device. The light radiated out from the surface emission type of semiconductor device is subjected to wavelength conversion, and a laser beam having an extreme short wavelength of the ultraviolet region can thereby be obtained.
With the first to eighth semiconductor laser apparatuses in accordance with the present invention, wherein laser oscillation is caused to occur by optical pumping, the problems do not occur in that doping impurities, and the like, diffuse due to heat generated by an electric current as in an electric current injection type of semiconductor laser device. Therefore, deterioration with the passage of time due to short-circuiting does not occur, and the reliability can be enhanced. Also, the problems do not occur in that the contact resistance increases due to diffusion of the impurities. Therefore, the threshold current can be reduced, and a high efficiency can be achieved.
Further, with the first to eighth semiconductor laser apparatuses in accordance with the present invention, wherein the light emission area of the surface emission type of semiconductor device is broad, the advantages over the electric current injection type of semiconductor laser device can be obtained in that the optical density is low, and therefore oscillation in the fundamental mode can be performed up to a high output power. Furthermore, deterioration of the end face due to an increased optical density can be restricted, and therefore a long service life can be obtained.
Also, with the first to eighth semiconductor laser apparatuses in accordance with the present invention, direct modulation of the semiconductor laser device can be performed through electrical modulation, and a quickly modulated laser beam can be obtained.
Further, with the first to eighth semiconductor laser apparatuses in accordance with the present invention, wherein the semiconductor laser device is employed as the pumping beam source, a laser apparatus can be obtained, which has a high efficiency and which is capable of being produced at a low cost and undergoing a CW operation.
Furthermore, with the first to eighth semiconductor laser apparatuses in accordance with the present invention, wherein optical pumping is utilized, the problems do not occur in that Mg acting as a doping agent, and the like, diffuse as in the ordinary electric current injection type of semiconductor laser device. Therefore, deterioration with the passage of time due to short-circuiting does not occur, and the service life of the semiconductor laser apparatus can be kept long.